Advanced microscopy characterisation and numerical modelling have been carried out to investigate
oxygen diffusion and crack growth in a nickel-based superalloy under fatigue-oxidation conditions.
Penetration of oxygen into the material and the associated internal oxidation, which leads to material
embrittlement and failure, have been found from Focused Ion Beam (FIB) examinations. Applied
fatigue loading tends to enhance the extent of internal oxidation for temperatures at 750°C and
above. Using a submodelling technique, finite element analyses of oxygen penetration at grain level
have been carried out to quantify the fatigue-oxidation damage and calibrate the diffusion parameters
based on the measurements of maximum depth of internal oxidation. The grain microstructure was
considered explicitly in the finite element model, where the grain boundary was taken as the primary
path for oxygen diffusion. A sequentially coupled mechanical-diffusion analysis was adopted to
account for the effects of deformation on diffusion during fatigue loading, for which the material
constitutive behaviour was described by a crystal plasticity model at grain level. Prediction of
oxidation-assisted crack growth has also been carried out at elevated temperature from the finite
2
element analyses of oxygen diffusion near a fatigue crack tip. A failure curve for crack growth has
been constructed based on the consideration of both oxygen concentration and accumulated inelastic
strain near the crack tip. The predictions from the fatigue-oxidation failure curve compared well with
the experimental results for triangular and dwell loading waveforms, with significant improvement
achieved over those predicted from the viscoplastic model alone.

Description:

This is the author’s version of a work that was accepted for publication in the journal Materials Science and Engineering: A
. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published at: http://dx.doi.org/10.1016/j.msea.2012.12.088